/Engine/Source/Runtime/Engine/Classes/Materials/MaterialExpressionStrata.h
class UMaterialExpressionStrataPostProcess : public [UMaterialExpressionStrataBSDF](API\Runtime\Engine\Materials\UMaterialExpressionStrataBSDF)
FExpressionInpu...
Color
The output color of the post process: it represents a color added over the back buffer, or a color multiplied if the Substrate blend mode is TransmittanceOnly.
FExpressionInpu...
Opacity
The coverage of the post process: the more the value is high, the less the back buffer will be visible.